Coordinated control for an arm prosthesis

ABSTRACT

A control method for an arm prosthesis having at least one powered joint and at least one inertial measurement sensor (IMS) includes determining a motion and an orientation of the arm prosthesis relative to the inertial reference frame based at least on an output of the IMS and generating control signals for the at least one powered joint based on the motion and the orientation of the prosthetic arm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 61/818,596, filed May 2, 2013 and entitled“Coordinated Control for an Arm Prosthesis”, the contents of which areherein incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to control of arm prostheses, and morespecifically to apparatus and methods for coordinating operation ofjoints in myoelectric arm prostheses.

BACKGROUND

In many conventional myoelectric arm prostheses with a powered elbowjoint, the configuration of the powered elbow joint is typicallycontrolled irrespective of the configuration of the shoulder joint, andthe wrist joint is typically controlled irrespective of theconfiguration of the other major joints in the arm. Further, in suchmyoelectric arm prostheses, the configuration of each joint in theprosthetic arm is typically controlled in a sequential manner (i.e., onejoint is moved at a time), until the arm is configured in a desiredposture.

The reason that conventional myoelectric prostheses are typicallyconfigured in a sequential manner is that the at least one joint of themyoelectric arm prosthesis is typically controlled with input from apair of electromyogram (EMG) measurements, each of which measures theelectrical activity resulting from a muscle contraction in a pair ofopposing muscles in the residual limb of the amputated arm. In the caseof an above-elbow amputation, the EMG is typically measured from thebiceps and triceps muscle groups. In the anatomical arm, the combinationof the pair of measurements provides a single bidirectional control forflexing or extending a given joint. Although the biceps and tricepsmuscles no longer act to flex and extend an anatomical elbow joint inabove-elbow amputees, filtered and rectified EMG measurements canprovide a real-time electrical signal proportional to the strength ofcontraction of the respective muscles in the residual limb. In mostmyoelectric arm prostheses, this electrical signal drives an elbow motorcontrol loop for the prosthesis, such that the angular velocity of theprosthetic elbow joint is proportional to the measured EMG, where EMG ismeasured from the biceps muscle group for flexion and EMG is measuredfrom the triceps muscle group for extension. Therefore, the angularspeed of the elbow joint is generally proportional to the strength ofcontraction. In the absence of muscle contraction, the elbow remainslocked at its current position (i.e., the joints of a myoelectricprosthetic arm are normally-locked). This control method can be referredto as differential, velocity-based EMG control.

In the case of an arm prosthesis with powered elbow and wrist joints,coordinated control of these joints is typically not possible since onlya single control signal (from the biceps and triceps) is available forcontrolling these multiple joints. As a result, the EMG control signalis typically switched between joints, resulting in the joints beingcontrolled in a sequential fashion. For example, the EMG frombiceps/triceps will first be used to move the prosthetic elbow joint.Thereafter, control may be switched to the wrist joint (typically bymomentarily co-contracting both the biceps and triceps in unison, ratherthan using them in a differential sense) and the EMG from thebiceps/triceps can adjust the angle of the wrist. A further momentaryco-contraction will switch control to a prosthetic hand, such that thesame EMG will open/close the hand. A subsequent momentary co-contractionwill cycle EMG control back to the elbow joint. As such, the sameagonist/antagonist muscle group (in this case biceps and triceps)provide myoelectric control of all of the joints and the hand of theprosthetic arm.

With respect to coordinated control of the powered elbow joint and theintact shoulder joint in an above-elbow prosthesis, the powered elbowunit could be moved in concert with the shoulder, but not without greatdifficulty. In particular, since substantial portions of both the bicepsand triceps extend over the shoulder joint (i.e., both are two-jointmuscle groups), movement of the intact shoulder also producesmyoelectric signals in the biceps and triceps. Therefore it isdifficult, if not impossible, particularly without elbow proprioception,for the amputee to provide EMG signals to control the prosthetic elbowjoint that are decoupled from EMG signals generated during use of theintact shoulder joint. As a result, the amputee typically resorts to theindependent, sequential configuring of the shoulder and elbow joints,which removes the interference that shoulder movement presents in thebiceps and triceps EMG signals. Therefore, above-elbow amputees aretypically forced to move all joints of the arm in a sequential manner.

SUMMARY

Embodiments of the invention concern systems and methods for controllingthe operation of arm prostheses. In particular, the present technologyis directed to systems and methods for the control of an arm prosthesis,where the prosthesis consists of at least one powered joint, and furthercomprises at least one inertial measurement sensor (IMS), where theinertial measurement sensor is used to measure the motion of theprosthetic limb, and by association the residual limb, relative to theinertial reference frame, and wherein the motion of the residual limb isused as a control input for controlling the movement of the at least onepowered joint.

In particular configurations, the at least one powered joint is an elbowjoint and the residual limb is the upper arm, where the inertialmeasurement sensor measures the motion of the upper arm, and where theangular movement of the elbow joint is controlled in relation to themeasured motion of the upper arm. The inertial measurement of the upperarm motion can be a measurement of upper arm spatial orientation and/orangular velocity with respect to an inertial reference frame.

In particular configurations, the elbow joint angular movement iscontrolled as a function of the upper arm spatial orientation, such thatthe elbow joint moves in extension when the upper arm orientationindicates that the elbow is moving away from the body, and such that theelbow joint moves in flexion when the upper arm orientation indicatesthat the elbow is moving closer to or toward the body. The movement ofthe elbow toward or away from the body can be indicated by the radialdistance of the elbow from the body centerline. Alternatively, themovement of the elbow toward or away from the body can be indicated bythe distance of the elbow joint from the body center projected onto apreselected plane relative to the body of the wearer, such as thesagittal plane, frontal plane, or mid-sagittal plane. Additionally, themovement of the elbow toward or away from the body can be indicated bythe distance of the elbow joint from the body center projected onto apreselected plane relative to the orientation of the axis of rotation ofthe elbow joint.

In some configurations, an elbow joint angular velocity can be caused byan instantaneous linear velocity of the elbow joint in a directionorthogonal to both the elbow axis of rotation and the long axis of theupper arm. Accordingly, the elbow joint angle can move in flexion whenthe instantaneous linear velocity is toward the body centerline and movein extension when the velocity is away from the body centerline.

In still other configurations, an angular velocity of the elbow jointcan be caused by an angular velocity of the upper arm with respect to aninertial reference frame. The angular velocity of the upper arm can bethe component of angular velocity along the rotational axis of the elbowjoint. Alternatively, the angular velocity of the upper arm can be thevector sum of angular velocity components in the plane orthogonal to thelong axis of the upper arm. In some cases, the angle of shoulderinternal/external rotation is used to modulate a gain between elbowjoint angular velocity and upper arm angular velocity.

In particular configurations, the elbow joint can be controlled suchthat the orientation of the forearm with respect to the inertialreference frame remains invariant for upper arm movement in the planeorthogonal to the axis of the elbow joint.

In the various configurations, electromyogram (EMG) control of the elbowjoint can be combined with IMS control of the elbow joint. In somecases, the EMG from the upper arm can be combined with measuredorientation of the upper arm from the IMS to cause movement of the elbowjoint. Further, a differential EMG elbow angular velocity control can besuperimposed onto the IMS control.

Additionally, a sustained co-contraction as indicated by EMG can be usedto prevent elbow joint movement or attenuate elbow joint movement inrelation to the strength of co-contraction.

In some configurations, an angular velocity of the upper arm can be usedto prevent differential EMG control of elbow joint movement.Alternatively, absence of angular velocity of the upper arm can switchcontrol of elbow joint motion to differential EMG control.

In some configurations, the prosthesis can be switched between thecoordinated control mode and a sequential control mode. This switchingcan be based on at least an EMG or an IMS event.

In some configurations, the at least one powered joint can include apowered wrist joint. The powered wrist joint can be controlled such thatthe orientation of the hand remains invariant relative to the inertialreference frame. Further, a co-contraction of muscles in the residuallimb can be used to select the coordinated wrist control mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of a prosthetic arm in accordancewith the present technology;

FIGS. 2 and 3 illustrates a user with the prosthetic arm of FIG. 1;

FIG. 4 shows a flowchart of steps in an exemplary method according tothe present technology; and

FIGS. 5A and 5B show a system embodiment suitable for implementing thecontrol system of the present technology.

DETAILED DESCRIPTION

The present invention is described with reference to the attachedfigures, wherein like reference numerals are used throughout the figuresto designate similar or equivalent elements. The figures are not drawnto scale and they are provided merely to illustrate the instantinvention. Several aspects of the invention are described below withreference to example applications for illustration. It should beunderstood that numerous specific details, relationships, and methodsare set forth to provide a full understanding of the invention. Onehaving ordinary skill in the relevant art, however, will readilyrecognize that the invention can be practiced without one or more of thespecific details or with other methods. In other instances, well-knownstructures or operations are not shown in detail to avoid obscuring theinvention. The present invention is not limited by the illustratedordering of acts or events, as some acts may occur in different ordersand/or concurrently with other acts or events. Furthermore, not allillustrated acts or events are required to implement a methodology inaccordance with the present invention.

This present technology is directed to a control methodology thatenables above-elbow amputees with myoelectric prostheses to effectcoordinated, simultaneous movements of their anatomical shoulder jointsand prosthetic elbow joints. In subjects with a healthy or intact arm,the major joints (i.e., shoulder, elbow, and possibly wrist) aretypically controlled simultaneously in order to achieve a desiredconfiguration of the arm. Configuring all joints simultaneously providesa number of important advantages relative to configuring themsequentially. The most obvious is that sequential configuration requiresmore time than simultaneous configuration of the joints, assuming thetime required to configure each joint is essentially invariant.Therefore, obtaining a desired posture with simultaneous configurationof the joints enables a faster movement of the arm. Perhaps moresignificantly, a user is often interested in following a given path withhis or her hand, rather than simply achieving a given final position ofthe hand. For example, in a reaching motion, or in opening a door or adrawer, the desired movement involves configuring the arm such that thehand follows a path or a trajectory, rather than simply obtaining asingle pose with the arm.

As is known in the study of robot manipulators, the ability to move theendpoint (in this case, the hand) of a multi-joint manipulator (in thiscase, the arm) along an arbitrary path requires the simultaneousmovement of multiple joints in the arm. For example, for a two-jointmanipulator consisting of a one-axis shoulder and one-axis elbow joint,moving the endpoint (i.e., hand) in a straight line path requires thesimultaneous movement of both the shoulder and elbow joints. If thejoints are moved sequentially, the path is instead constrained to movealong one of two arc-shaped paths (an arc with a center located eitherat the shoulder or elbow, depending on which joint is being sequentiallymoved). Thus, the inability to configure multiple joints in a serialmanipulator (i.e., arm) simultaneously increases the time to achieve agiven configuration, and restricts severely the ability to move the handalong a generalizable path or trajectory.

In view of the limitations of existing myoelectric prostheses, thepresent technology is directed to a control methodology that enablesabove-elbow amputees with myoelectric prostheses to effect coordinated,simultaneous movements of their anatomical shoulder joints andprosthetic elbow joints. Although the various embodiments will bedescribed primarily with respect to coordinating the control of aprosthetic elbow joint in an above-elbow myoelectric arm with themovement of the intact shoulder joint, the methodology of the presenttechnology is also more broadly applicable to above-elbow andbelow-elbow myoelectric arms with wrist joints.

Turning first to FIG. 1, there is shown an above-elbow myoelectric armprosthesis 100 in accordance with the present technology. As shown inFIG. 1, the arm prosthesis 100 includes an upper arm portion 102, with asocket 104 for receiving a residual limb, a forearm portion 106, and apowered elbow joint 108 rotatably coupling the forearm portion 106 andthe upper arm portion 102. The powered elbow joint 108 can be configuredto provide extension or flexion of the arm prosthesis 100.

A distal end of the forearm portion 106, the arm prosthesis 100 caninclude a hand portion 110. The hand portion 110 can include one or morepowered joints. Further, although the hand portion 110 is shown as ahand-type terminal device, the hand portion 110 can be anon-anthropomorphic terminal device, such as a hook-type device.

The hand portion 110 can be coupled via a wrist joint 112. In someconfigurations, the wrist joint 112 can be passive. However, in otherconfigurations, the wrist joint 112 can be powered as well and providemotion along one or more degrees of freedom.

As noted above, the arm prosthesis 100 can be controlledmyoelectrically. Accordingly, the arm can include EMG sensors 114 fordetecting EMG signals generated by different muscle groups.Additionally, the arm prosthesis 100 can include a controller 116 forreceiving the EMG signals from EMG sensors 114 and for generatingcontrol signals for the elbow joint 108 and, if needed, for a wristjoint 112 and hand 110.

In addition to the above-mentioned components, which provide basicmyoelectric operation of arm prosthesis 100, as previously described,the arm prosthesis 100 can also include components to support thecoordinated control of joints in accordance with the present technology.

In particular, the arm prosthesis can include an inertial measurementunit (IMS) 118 that can be used to compute in real-time the motion(relative to an inertial reference frame) of the upper arm portion 102,and therefore estimate the motion of wearer's residual limb. As usedherein, the motion information obtained based on the IMS 118 canencompass one or more of displacement or position, direction, velocity,acceleration, and time. In a particular embodiment, the IMS is locatedon the forearm portion 106 of arm prosthesis 100, although it can belocated on any part of arm prosthesis 100. In some embodiments, IMS 118can comprise a 3-axis gyroscope from which an angular velocity can becomputed in multiple directions or axes. In other embodiments, the IMS118 can comprise a single-axis gyroscope from which the angular velocitycan be along a single direction or axis. In still other embodiments, IMS118 can comprise accelerometers, gyroscopes, and potentiallymagnetometers. For example, in one particular embodiment, IMS 118 is anine-axis IMS that includes a 3-axis accelerometer, a 3-axis gyroscope,and a 3-axis magnetometer. The data from these elements can then be usedby controller 116 to compute the 3-dimensional orientation of the upperarm portion 102 and thus estimate the 3-dimensional orientation of aresidual limb in socket 104 in real-time. The computation for anine-axis IMS, such as IMS 118, is described below.

In general, a 3-axis magnetometer provides a low-frequency measure ofthe direction of the magnetic north vector (relative to the Earth, orinertial-reference frame). The 3-axis accelerometer provides alow-frequency measure of the direction of the gravity vector (relativeto the Earth frame) and the 3-axis gyroscope provides angular velocitiesabout each of the IMS's principal axes. The measured orientations of themagnetic north and gravity vectors can be used to compute an orthonormalbasis of vectors (u₁, u₂, u₃) of the reference frame for the IMU. Thisorthonormal basis represents the three-dimensional orientation of theIMU relative to the inertial reference frame (IRF), and can be computedfrom:

u₁=g  (1)

u ₂ =g×m  (2)

u ₃ =u ₁ ×u ₂  (3)

where g is the measured gravity vector and m is the measured magneticnorth vector.

Concatenating this set of vectors forms a rotation matrix whichrepresents the steady state orientation of the IMS. Since theaccelerometer and magnetometer generally provide low-frequency(essentially steady-state) measurements, this information can becombined with the measured angular velocity from the gyroscope toprovide high-frequency measurement.

Specifically, the gyroscope provides angular velocities about eachprincipal axis of the IMS, which are integrated to calculate anestimation of the angular position of the IMS. Since the integration mayresult in drift over a prolonged period, only the high-frequencyinformation from the gyroscope is used. By using a complementary filterapproach to combine the low-frequency information from the magnetometerand accelerometer with the high-frequency information from thegyroscope, the three sensing modalities of the 9-axis IMS can provide asingle rotation matrix with good accuracy and dynamic response, thusproviding a real-time measurement of IMS orientation.

Referring back to FIG. 1, the IMS 118 is shown as being located on upperarm portion 102 of arm prosthesis 100. However, since all configurationangles within arm prosthesis 100 are known, the motion of upper armportion 102 can be computed, and that of residual arm as well,regardless of the location of the IMS 118 in arm prosthesis 100. Thus,the IMS 118 can be located anywhere on arm prosthesis 100 in the variousembodiments. For example, if the IMS 118 is situated on the forearm ofthe arm prosthesis, and if the elbow joint angle is measured (e.g., withan angular position sensor such as a rotary encoder), the orientationand motion of the wearer's upper arm (i.e., residual limb) can bedetermined relative to the inertial reference frame. Using theorientation or angular velocity information from the IMS 118, thecontroller 116 can then be used to coordinate motion of the poweredjoints in arm prosthesis 100 with that of the intact shoulder joint, asillustrated in FIG. 2. In particular, assuming the upper body 202 (i.e.,torso) of the user remains relatively stationary in or near a knownconfiguration (e.g., a center line 204 of the upper body isapproximately parallel to a gravity vector 206), the configuration ormovement of the shoulder joint 209 can also be estimated by thecontroller 116 in real-time based on the orientation or angular velocityinformation 208 obtained using IMS 118 for the residual limb 210. Inparticular, the IMS information 208 can be utilized by the controller116 to extrapolate shoulder movement in rotation 212,abduction/adduction 214, and/or flexion/extension. Based on thisestimate of shoulder motion and/or configuration, the rotation 218 ofthe powered elbow joint 108 can be specified by controller 116 such thatit moves in a coordinated fashion with the shoulder joint. Thus, thecontroller 116 can be configured to provide movement coordinationbetween the powered elbow joint 118 and the (intact) shoulder joint 209.This coordinated movement can be independent of the EMG measurementsfrom the residual limb, or can be modulated by or coordinated with theEMG input patterns to modify the pattern of coordination between theelbow and shoulder joints.

In one particular embodiment, the controller 116 can be configured tooperate the arm prosthesis 100 in a reaching mode. In the reaching mode,the powered elbow joint 118 is flexed or extended in relation to theestimated distance 302 between a location 307 of the powered elbow 118and approximate centerline 204 of the body 202. In the reaching mode, itis also important to distinguish between the elbow joint location 307,which is a function of the upper arm orientation (and therefore afunction of shoulder angle), and the elbow joint angular position 306,which is the angle formed between the forearm portion 106 and upper armportion 102. The powered elbow joint location 307 can be identified bythree Cartesian coordinates with respect to a reference 308 alongcenterline 204, while the elbow joint angle 306 (or elbow angle) is ascalar (since the powered elbow joint 108 is assumed to be a hinge, andthus has a single degree of freedom). The elbow joint angle 306 isdescribed anatomically as elbow flexion and extension, where flexiondecreases the angle between the forearm portion 106 and upper armportion 102, and extension increases it. The shoulder joint 209 isassumed to be a ball joint, and therefore has three degrees of freedom,described by flexion/extension, abduction/adduction, andinternal/external rotation (as shown in FIG. 2).

The location 307 of the powered elbow joint 108 relative to the bodycenterline 204 can be regarded as the elbow position in the Cartesianframe, while the angles of the elbow joint 108 and the shoulder joint209 can be regarded as the elbow and shoulder joint angles in theconfiguration frame. Note that shoulder flexion/extension andabduction/adduction in the configuration frame generally result in elbowmovement in the Cartesian frame, while shoulder internal/externalrotation in the configuration frame results in re-orientation of theelbow joint in the Cartesian frame, but not elbow joint movement throughthe Cartesian frame.

In the reaching mode, if the shoulder joint 209 moves the powered elbowjoint 108 away from the body 202 (in the Cartesian frame), thecontroller 116 can cause the powered elbow joint 108 to be extended (inthe configuration frame) in relation to the linear distance between theelbow and body centerline. If the shoulder joint 209 moves the poweredelbow joint 108 toward the body 202, the controller 116 configures thepowered elbow joint 108 to be flexed in relation to the distance betweenthe powered elbow joint 108 and the centerline 204. The estimateddistance 309 can then be computed by the control 116 as a function ofthe orientation of the upper arm portion 201 (which can be used toapproximate shoulder configuration) and the known length 310 from theintact shoulder joint 209 to the powered elbow joint 108. Alternatively,an alternate estimation is to use only the spatial orientation of theupper arm portion 102 to estimate the distance between the powered elbowjoint 108 and centerline 204. In this approach, the elbow angularvelocity is essentially proportional to the component of velocity withwhich the powered elbow joint is moving away from or towards thecenterline 204 (where away from results in an extensive angular velocityand towards results in a flexive angular velocity).

The operation of the reaching mode can be further refined by using theorientation of the powered elbow joint 108 in relation to the shoulderjoint 209 in order to further specify the action for the powered elbowjoint 108. In particular, the movement of the powered elbow joint 108can occur in relation to the projection of shoulder joint movement ontothe plane orthogonal to the elbow joint axis of rotation (which is theplane containing the forearm portion 106 and the upper arm portion 102).In this manner, only shoulder joint movement in substantially the sameplane as potential elbow joint movement will cause the controller 116 togenerate coordinated movement in the powered elbow joint 108. Therefore,detecting reaching with the shoulder joint 209 in a plane substantiallyorthogonal to the current axis of elbow joint rotation 218 will causethe controller 116 to generate simultaneous coordinated reaching withthe powered elbow joint 108, while reaching with the shoulder joint 209in a substantially different plane will not cause the controller 116 togenerate a simultaneous coordinated movement of the powered elbow joint108. In this manner, the user can control whether or not coordinatedreaching, using the powered elbow joint 108, will occur by orienting theshoulder appropriately. This approach is essentially the same as usingthe rotation about the long axis of the humerus bone (i.e.,internal/external rotation 212 of the shoulder) to control the extent towhich elbow flexion/extension is linked to elbow movement in theinertial reference frame.

In some configurations, the controller 116 can be configured such thatthe coordinated action between the shoulder joint 209 and powered elbowjoint 108 only occurs in a preselected plane. For example, thecontroller 116 can be configured to provide coordinated action only whenthe arm prosthesis 100 is oriented essentially in the sagittal plane.Alternatively, the controller 116 can be configured to coordinate actiononly when the arm prosthesis 100 is oriented essentially in the frontalor mid-sagittal planes. In all cases, the controller 116 utilizes themeasured movement of the upper arm 104 to generate flexion or extensionof the powered elbow joint 108, where the extra degrees-of-freedom inthe shoulder joint 209 (three in the shoulder relative to one in theelbow) are used to modulate the relationship between movement of theupper arm portion 104 and movement of the powered elbow joint 108.

In addition to using the IMS 118 to command flexion and extension of thepowered elbow joint 108, the controller 116 can also be configured tocombine an IMS coordinated control approach with EMG measurement fromthe upper arm (i.e., from the biceps and triceps muscle groups) tomodify the IMS coordinated control approach. In one embodiment, standard

EMG control, in which the differential amplitude of the EMG signals isused to command an angular velocity of the powered elbow joint 108, canbe superimposed on the IMS coordinated control approach, which has theeffect of moderating or modifying the coordinated control action bysuperimposing an elbow angular velocity command from the EMG onto theelbow angular velocity command from the IMS.

In another embodiment of the controller, a sustained co-contraction ofthe biceps and triceps musculature (as measured via EMG sensors 114) canbe used by the controller 116 to lock out the influence of the IMS 118,such that movement of the upper arm portion 104 does not affect movementof the powered elbow joint 108 while the user is co-contractingmusculature in the residual limb. Note that this approach has abiological analog, since a healthy individual will generally co-contractagonist/antagonist musculature in order to prevent a joint from moving.

In a variation of this approach, the strength of co-contraction (asmeasured via EMG sensor 114) can be used by the controller 116 toinversely modulate the gain of the previously described IMS coordinatedcontrol approach (e.g., modulate the gain relating the extension andflexion angular velocity of the powered elbow joint 108 to the componentof linear velocity away from and toward, respectively, the bodycenterline 204). A strong co-contraction would essentially cause thecontroller 116 to zero the gain (i.e., lock the powered elbow joint 108,and decouple motion of the powered elbow joint 108 from motion in theshoulder joint 209), while a weak co-contraction would cause thecontroller 116 to slightly attenuate the gain (i.e., maintain butslightly lessen the coupling between motion in the shoulder joint andmotion in the powered elbow joint 108).

In some embodiments, movement of the upper arm portion 104 (as detectedby IMS 118) can be used by the controller 116 to effectively lock outdifferential (velocity-based) EMG control of the powered elbow joint108. Additionally, the absence of motion in the shoulder joint 209 (andthus in upper arm portion 104) can be used by the controller 116 toenable standard EMG-based differential velocity control. Therefore, whenthe controller 116 detects that the shoulder joint 209 (and the upperarm portion 104) is moving, the powered elbow joint 108 is controlledusing a IMS-based coordination controller (potentially modulated by EMGco-contraction), and when the shoulder joint 209 (and the upper armportion 104) are not moving, the controller 116 reverts to the standardEMG-based differential velocity control.

With this control architecture implemented in controller 116, if theuser co-contracts strongly while moving the upper arm portion 104, theIMS controller is locked out and the controller 116 essentially operatesas a standard differential EMG velocity controller. By lessening thestrength of the co-contraction during movement of the upper arm portion104 (and the shoulder joint 209), the controller 116 complements thetraditional (differential EMG) control method with the previouslydescribed IMS-based coordinated control approach. In this manner, theuser can independently control movement of the powered elbow joint 108when desired, and can alternatively leverage coordinated control of theshoulder joint 209 and powered elbow joint 108 movement when desired.

In a different embodiment, the controller 116 can be configured so thatthe coordination between the powered elbow joint 108 and shoulder 209can be such that the forearm portion 102 remains at a fixed orientationrelative to the inertial reference frame for shoulder movement in theplane orthogonal to the axis 218 of the powered elbow joint 108. Forexample, if the axis 218 of the powered elbow joint 108 is orthogonal tothe vertical, then movement of the shoulder joint 208 such that theupper arm portion 104 moves in the vertical plane will control thepowered elbow joint 108 such that the forearm portion 102 remains at thesame angle with respect to the vertical. If the axis 218 of the poweredelbow joint 108 is orthogonal to the horizontal plane, movement of theshoulder that moves the upper arm in the horizontal plane will maintainthe orientation of the forearm portion 104 relative to an inertialreference frame in the horizontal plane. When moved in a differentplane, the projection of the angle of the forearm portion 104 withrespect to the inertial reference frame onto the plane orthogonal to theaxis 218 of the powered elbow joint 108 will remain invariant.

Further, in this embodiment, the prescribed angle at which the forearmportion 104 remains invariant with respect to the inertial referenceframe can be adjusted by the controller 116 by using EMG input from theresidual limb in a manner similar to the typical myoelectric control ofthe powered elbow joint 108. Thus, EMG control of the angle of thepowered elbow joint 108 can be superimposed onto the coordinated controlof the powered elbow joint 108, such that the movement of the poweredelbow joint 108 is both a function of EMG and movement of the shoulderjoint 209.

In all embodiments of the control methodology of the present technology,it may be useful for the controller 116 to be configured to allow theuser to switch between a coordinated control mode and a strictlysequential control mode. In a preferred embodiment, the control approachwill automatically switch into standard differential EMG velocitycontrol in the absence of movement of shoulder joint 209 (as detectedvia IMS 118). In another embodiment, the user can switch between thesemodes by a co-contraction pulse of both the biceps and triceps muscles,which is a commonly used method for switching control between joints ina multi-joint arm or for selecting various modes of operation. Theswitching signal can be a single co-contraction or a pattern of multipleco-contractions.

Alternatively, the user can switch between modes via the IMS 118. Inparticular, the user can perform a specific movement and the IMS 118then generates a set of signals that causes the controller 116 switchbetween modes. For example, the user can perform a sudden abduction ofthe shoulder joint 209, which can be used to indicate that the userwould like to switch between the coordinated and sequential controlmodes. Alternatively, information from the two sensors can be combined,such that switching is indicated by a co-contraction (as measured viaEMG 114) and simultaneous sudden movement of the shoulder joint (asmeasured by the IMS 118).

In some embodiments, the arm prosthesis 100 can contain a powered wristjoint 112, as described above with respect to FIG. 1. In suchembodiments, the IMS 118 can be used to determine the orientation of theprosthetic hand 110 relative to the inertial reference frame. Forexample, as noted above, the configuration of the arm prosthesis 100 isgenerally known and the orientation of its various components cantherefore be determined based off a single IMS. However, the presenttechnology is not limited in this regard and an IMS can be additionallyprovided for prosthetic hand 110.

When switched into a wrist control mode, the joints of the armprosthesis 100 can be coordinated with the movement of the shoulderjoint 209 to maintain the prosthetic hand 110 in a prescribedorientation. For example, when the powered elbow joint 108 is fullyextended, the prosthetic hand 110 can be rotated about the axis of thearm prosthesis 100 either by pronation supination of the wrist or byinternal and external rotation of the shoulder. In this coordinatedcontrol mode, if the shoulder joint 209 were internally or externallyrotated, the powered wrist joint 112 would provide an equal and oppositewrist pronation or supination, such that the hand would not rotaterelative to the inertial reference frame. Flexion and extension or ulnarand radial deviation can be controlled similarly. This mode of operationcan be switched by an EMG or IMS event, or some combination thereof. Ina preferred embodiment, a sustained EMG co-contraction would cause thewrist to operate in this mode for the duration of the sustainedco-contraction.

Now turning to FIG. 4, there is shown a flowchart of steps in anexemplary method 400 for coordinated control of a prosthetic arm inaccordance with the present technology. The method begins at step 402.At step 402, the prosthetic arm prosthesis 100 can be initialized. Insome configurations, this merely involves the powering the controller116 in arm prosthesis 100. Optionally, this can involve manuallyselecting a mode of operation. That is, a user could select to operatethe arm prosthesis 100 in a conventional EMG mode or allow the armprosthesis 100 to auto-select between the conventional EMG mode and acoordinated control mode based on motion, orientation, and configurationinformation for the arm prosthesis 100, as described above. In suchconfigurations, a mechanical switch can be provided on arm prosthesis100, the mode can be selected at step 404 based on co-contractionsdetected by EMG sensors 114, or some other methodology can be providedfor setting this operation mode at step 404.

In the case of manual mode selection, the method 400 can thereafterproceed to step 404. At step 404 it is determined whether the EMG modehas been manually selected or not. If the EMG mode has been manuallyselected at 404, the method can proceed to step 412, discussed infurther detail below. Otherwise, the method proceeds to step 406.

After the initialization of the prosthetic arm prosthesis 100 at step402 and, optionally, the determination at step 404 that auto-selectionof mode is desired, the method can proceed to step 406. At step 406,sensor information for the prosthetic arm prosthesis 100 is received bycontroller 116. This sensor information can include, for example,signals from IMS 118, signals from EMG sensors 114,configuration/position information for joints in arm prosthesis 100(e.g., powered elbow joint 108, wrist joint 112, and/or joints inprosthetic hand 110), or any combination thereof. Once the sensorinformation is received by controller 116 at step 406, the methodproceeds to step 408. At step 408, the current motion, orientation, andconfiguration of arm prosthesis 100, and thus that of the residual limbby way of upper arm portion 102, with respect to the inertial referenceframe, is computed.

Thereafter, the information obtained at step 408 for the arm prosthesis100 and the residual limb is utilized at step 410 to auto-select a modeof operation for the arm prosthesis 100. As noted above, the armprosthesis 100 can be operated in a coordinated control mode or aconventional EMG control mode based on the orientation of the armprosthesis 100 and/or control signals being received (e.g., signals fromEMG sensors 114). Further, as also noted above, the type of coordinatedcontrol or even the type of conventional EMG control to be provided forarm prosthesis 100 can also vary based on the current motion,orientation, or the configuration of the arm prosthesis 100.

Once the control mode is auto-selected at step 408 (or a manual EMGcontrol mode is determined at step 404), the control signals appropriatefor the current control mode can be generated at step 412 and theprosthetic arm prosthesis 100 is operated. In an EMG control mode, thejoints are operated conventionally, based on signals from EMG sensors114. In a coordinated control mode, the control signals can be basedsolely on the current motion, orientation, and configuration of the armprosthesis 100. However, as also discussed above, these control signalscan also be based on a combination of the current motion, orientation,and configuration and the control signals provided by the user via EMGsensors 114. For example, as discussed above, EMG signals can be used tomodulate or modify the motion in a particular mode.

Thereafter, steps 406, 408, 410, and 412 are repeated continuously.Optionally, after step 412, a determination can be made as to whetherthe current operation mode has changed. That is, whether the controllerdetects the user manually selecting going to the EMG control mode or theauto-select mode of operation. If there is no change, the methodproceeds to repeat method 400 starting with step 406. Otherwise, themethod proceeds to repeat method 400 starting with step 404.

FIG. 5A, and FIG. 5B illustrate exemplary possible system embodimentsfor a controller for carrying out the various embodiments in accordancewith the present technology. The more appropriate embodiment will beapparent to those of ordinary skill in the art when practicing thepresent technology. Persons of ordinary skill in the art will alsoreadily appreciate that other system embodiments are possible.

FIG. 5A illustrates a conventional system bus computing systemarchitecture 500 wherein the components of the system are in electricalcommunication with each other using a bus 505. Exemplary system 500includes a processing unit (CPU or processor) 510 and a system bus 505that couples various system components including the system memory 515,such as read only memory (ROM) 520 and random access memory (RAM) 525,to the processor 510. The system 500 can include a cache of high-speedmemory connected directly with, in close proximity to, or integrated aspart of the processor 510. The system 500 can copy data from the memory515 and/or the storage device 530 to the cache 512 for quick access bythe processor 510. In this way, the cache can provide a performanceboost that avoids processor 510 delays while waiting for data. These andother modules can control or be configured to control the processor 510to perform various actions. Other system memory 515 may be available foruse as well. The memory 515 can include multiple different types ofmemory with different performance characteristics. The processor 510 caninclude any general purpose processor and a hardware module or softwaremodule, such as module 1 532, module 2 534, and module 3 536 stored instorage device 530, configured to control the processor 510 as well as aspecial-purpose processor where software instructions are incorporatedinto the actual processor design. The processor 510 may essentially be acompletely self-contained computing system, containing multiple cores orprocessors, a bus, memory controller, cache, etc. A multi-core processormay be symmetric or asymmetric.

To enable user interaction with the computing device 500, an inputdevice 545 can represent any number of input mechanisms, such as amicrophone for speech, a touch-sensitive screen for gesture or graphicalinput, keyboard, mouse, motion input, speech and so forth. An outputdevice 535 can also be one or more of a number of output mechanismsknown to those of skill in the art. In some instances, multimodalsystems can enable a user to provide multiple types of input tocommunicate with the computing device 500. The communications interface540 can generally govern and manage the user input and system output.There is no restriction on operating on any particular hardwarearrangement and therefore the basic features here may easily besubstituted for improved hardware or firmware arrangements as they aredeveloped.

Storage device 530 is a non-volatile memory and can be a hard disk orother types of computer readable media which can store data that areaccessible by a computer, such as magnetic cassettes, flash memorycards, solid state memory devices, digital versatile disks, cartridges,random access memories (RAMs) 525, read only memory (ROM) 520, andhybrids thereof.

The storage device 530 can include software modules 532, 534, 536 forcontrolling the processor 510. Other hardware or software modules arecontemplated. The storage device 530 can be connected to the system bus505. In one aspect, a hardware module that performs a particularfunction can include the software component stored in acomputer-readable medium in connection with the necessary hardwarecomponents, such as the processor 510, bus 505, display 535, and soforth, to carry out the function.

FIG. 5B illustrates a computer system 550 having a chipset architecturethat can be used in executing the described method and generating anddisplaying a graphical user interface (GUI). Computer system 550 is anexample of computer hardware, software, and firmware that can be used toimplement the disclosed technology. System 550 can include a processor555, representative of any number of physically and/or logicallydistinct resources capable of executing software, firmware, and hardwareconfigured to perform identified computations. Processor 555 cancommunicate with a chipset 560 that can control input to and output fromprocessor 555. In this example, chipset 560 outputs information tooutput 565, such as a display, and can read and write information tostorage device 570, which can include magnetic media, and solid statemedia, for example. Chipset 560 can also read data from and write datato RAM 575. A bridge 580 for interfacing with a variety of userinterface components 585 can be provided for interfacing with chipset560. Such user interface components 585 can include a keyboard, amicrophone, touch detection and processing circuitry, a pointing device,such as a mouse, and so on. In general, inputs to system 550 can comefrom any of a variety of sources, machine generated and/or humangenerated.

Chipset 560 can also interface with one or more communication interfaces590 that can have different physical interfaces. Such communicationinterfaces can include interfaces for wired and wireless local areanetworks, for broadband wireless networks, as well as personal areanetworks. Some applications of the methods for generating, displaying,and using the GUI disclosed herein can include receiving ordereddatasets over the physical interface or be generated by the machineitself by processor 555 analyzing data stored in storage 570 or 575.Further, the machine can receive inputs from a user via user interfacecomponents 585 and execute appropriate functions, such as browsingfunctions by interpreting these inputs using processor 555.

It can be appreciated that exemplary systems 500 and 550 can have morethan one processor 510 or be part of a group or cluster of computingdevices networked together to provide greater processing capability.

For clarity of explanation, in some instances the present technology maybe presented as including individual functional blocks includingfunctional blocks comprising devices, device components, steps orroutines in a method embodied in software, or combinations of hardwareand software.

In some embodiments the computer-readable storage devices, mediums, andmemories can include a cable or wireless signal containing a bit streamand the like. However, when mentioned, non-transitory computer-readablestorage media expressly exclude media such as energy, carrier signals,electromagnetic waves, and signals per se.

Methods according to the above-described examples can be implementedusing computer-executable instructions that are stored or otherwiseavailable from computer readable media. Such instructions can comprise,for example, instructions and data which cause or otherwise configure ageneral purpose computer, special purpose computer, or special purposeprocessing device to perform a certain function or group of functions.Portions of computer resources used can be accessible over a network.The computer executable instructions may be, for example, binaries,intermediate format instructions such as assembly language, firmware, orsource code. Examples of computer-readable media that may be used tostore instructions, information used, and/or information created duringmethods according to described examples include magnetic or opticaldisks, flash memory, USB devices provided with non-volatile memory,networked storage devices, and so on.

Devices implementing methods according to these disclosures can comprisehardware, firmware and/or software, and can take any of a variety ofform factors. Typical examples of such form factors include laptops,smart phones, small form factor personal computers, personal digitalassistants, and so on. Functionality described herein also can beembodied in peripherals or add-in cards. Such functionality can also beimplemented on a circuit board among different chips or differentprocesses executing in a single device, by way of further example.

The instructions, media for conveying such instructions, computingresources for executing them, and other structures for supporting suchcomputing resources are means for providing the functions described inthese disclosures.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Numerous changes to the disclosedembodiments can be made in accordance with the disclosure herein withoutdeparting from the spirit or scope of the invention. Thus, the breadthand scope of the present invention should not be limited by any of theabove described embodiments. Rather, the scope of the invention shouldbe defined in accordance with the following claims and theirequivalents.

Although the invention has been illustrated and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art upon the reading andunderstanding of this specification and the annexed drawings. Inaddition, while a particular feature of the invention may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Furthermore, to the extent that the terms “including”,“includes”, “having”, “has”, “with”, or variants thereof are used ineither the detailed description and/or the claims, such terms areintended to be inclusive in a manner similar to the term “comprising.”

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. Also, theterms “about”, “substantially”, “essentially”, and “approximately”, asused herein with respect to a stated value, property, or condition areintend to indicate being within 20% or less of the stated value,property, or condition unless otherwise specified above. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

1. A method for the control of an arm prosthesis having at least onepowered joint and at least one inertial measurement sensor (IMS), themethod comprising: determining a motion of the arm prosthesis relativeto the inertial reference frame based at least on an output of the IMS;generating control signals for the at least one powered joint based onthe motion and the orientation of the prosthetic arm.
 2. The method ofclaim 1, wherein the at least one powered joint comprises a poweredelbow joint, wherein the IMS measures the motion of an upper arm portionof the arm prosthesis, and wherein the generating the control signalscomprises controlling an angular movement of the powered elbow jointbased on the motion of the upper arm.
 3. The method of claim 2, whereinthe generating of control signals comprises: determining a motion of thepowered elbow joint with respect to a body of a user based on theorientation and motion of the arm prosthesis with respect to the body;configuring the control signals to move the powered elbow joint inextension when the powered elbow joint is moving away from the body; andconfiguring the control signals to move the powered elbow joint inflexion when the powered elbow joint is moving closer toward the body.4. The method of claim 3, wherein determining the motion of the poweredelbow joint with respect to the body comprises determining a change inat least one of a radial distance from the powered elbow joint to atleast one of a centerline of the body or a distance of the powered elbowjoint from a preselected plane relative to the body.
 5. The method ofclaim 2, wherein the generating of control signals comprises:determining a velocity vector for the powered elbow joint with respectto a body of a user in a direction orthogonal to both an axis ofrotation of the powered elbow joint and a long axis of the upper armportion based on the orientation and motion of the arm prosthesis withrespect to the body; configuring the control signals to move the poweredelbow joint in extension when the velocity vector points away from thebody; and configuring the control signals to move the powered elbowjoint in flexion when the velocity vector points towards the body. 6.The method of claim 2, wherein the generating of control signalscomprises: determining an angular velocity of the upper arm portion withrespect to the inertial reference frame; and configuring the controlsignals to move the powered elbow joint according to the angularvelocity.
 7. The method of claim 6, where the angular velocity of theupper arm is the component of angular velocity along the rotational axisof the powered elbow joint.
 8. The method of claim 6, where the angularvelocity of the upper arm is the component of angular velocityorthogonal to the long axis of the upper arm.
 9. The method of claim 6,further comprising determining an angle of internal/external shoulderrotation, and wherein the configuring further comprises modulating again between the angular velocity of the upper arm portion and anangular velocity for the powered elbow joint
 10. The method of claim 2,wherein the generating of control signals further comprises: determiningwhether the upper arm portion is moving in a plane orthogonal to theaxis of the powered elbow joint; and upon determining that the upper armportion is moving in a plane orthogonal to the axis of the powered elbowjoint, configuring the control signals to maintain an orientation of aforearm portion of the arm prosthesis invariant.
 11. The method of claim1, wherein the control signals also comprise electromyogram (EMG)signals, and wherein the generating of the control signals furthercomprises modulating an amount of motion of the at least one poweredjoint based on the EMG signals.
 12. The method of claim 11, where asustained co-contraction as indicated by EMG attenuates the amount ofmotion based on a strength of the co-contraction.
 13. The method ofclaim 11, wherein a sustained co-contraction as indicated by EMGprevents movement of the at least one powered joint.
 14. The method ofclaim 1, further comprising: selecting a mode of operating the at leastone powered joint based at least on the motion of the upper arm portion;and configuring the control signals based on the selected mode.
 15. Themethod of any of claim 14, wherein the selecting of the mode comprises:detecting whether an angular velocity of an upper arm portion of theprosthetic arm is non-zero; and upon detecting that the angular velocityof the upper arm portion is non-zero, choosing the mode to be a modethat prevents differential electromyogram control of the at least onepowered joint; and upon detecting that the angular velocity of the upperarm portion is substantially zero, choosing the mode to be a mode fordifferential electromyogram control of the at least one powered joint.16. The method of claim 14, wherein the selecting of the mode comprisesselecting between a coordinated control mode and a sequential controlmode for the at least one powered joint.
 17. The method of claim 16,where the selecting is based on at least one of an electromyogram eventor an IMS event.
 18. The method of claim 1, where the at least onepowered joint is a powered wrist joint between a forearm portion and ahand portion of the prosthetic arm.
 19. The method of claim 17, wherethe generating of the control signals comprises configuring the controlsignals for the powered wrist joint to maintain an orientation of thehand portion invariant relative to the inertial reference frame.
 20. Acomputer-readable medium having stored thereon a computer program forcontrolling a prosthetic arm, the computer program comprising aplurality of instructions for causing a control system for a prostheticarm comprising an upper arm portion, a forearm portion, a powered elbowjoint, and an inertial measurement sensor, to perform steps comprising:determining a motion of the arm prosthesis relative to the inertialreference frame based at least on an output of the IMS; and generatingcontrol signals for the at least one powered joint based on the motionand the orientation of the prosthetic arm.
 21. A control system for aprosthetic arm comprising an upper arm portion, a forearm portion, apowered elbow joint, and an inertial measurement sensor, the controlsystem comprising: a processor; and a computer readable medium, havingstored thereon a plurality of instructions for causing the processor toperform steps comprising: determining a motion of the arm prosthesisrelative to the inertial reference frame based at least on an output ofthe IMS; and generating control signals for the at least one poweredjoint based on the motion and the orientation of the prosthetic arm.